Rubber-reclaiming oil



Patented Aug. 24, 1948 RUBBER-RECLAHVIIN G OIL Charles H. Campbell,Kent, Ohio, and Robert W.

Ostermayer, Clairton, Pa.; said Ostermayer assignor to said Campbell NoDrawing. Application July 16, 1945, Serial No. 605,434

4 Claims. 1

This invention relates to a. rubber-reclaiming oil and to the method ofits use in reclaiming scrap rubber, and the application herein is acontinuation-in-part of our application, Serial No. 341,140, filed June18, 1940.

In one currently practiced process of reclaiming rubber, the scraprubber which is the stock to be reclaimed is brought into a condition ofrelatively fine division; and after it has been screened to removeassociated fibrous material it is subjected to heat and pressure in thepresence of moisture. Usually an alkali, such as sodium hydroxide, ispresent during the treatment of the stock with heat and pressure, forthe purpose of breaking down any fabric remaining with the rubber and toreduce the percentage of sulphur in the stock. It is standard practicealso to include with the scrap rubber during the treatment with heat,pressure and alkali, an oil which serves to soften and swell the rubberand assists materially in bringing it into condition for reworking. Itis to be understood that in the modern reclaiming processes to whichreference is here made the function of the reclaiming oil is not todissolve the rubber for subsequent recovery by precipitation, orcoagulation, but that its function is to swell and soften the rubber forreworking.

Following the digestion treatment of the scrap rubber, the stock isfurther processed prior to recompounding and working by blowing down thedigestor in which the stock has been prepared, by removing as muchcaustic solution as possible by pressure washing with water and steam,and by evaporative drying. The substantial equivalents of these latterprocess steps sometimes are employed. It is in the composition of thereclaiming oil for softening and swelling the rubber that the inventionof this present method primarily resides. It is of importance that, whenimder the conditions of the process the rubber has been opened up andinitially swelled by heat and pressure, the reclaiming oil be able so topenetrate the rubber and to have such an enduring softening and furtherswelling effect thereon as to give effectiveness to the fundamentaltreatment with heat and pressure. It is thus by the eifect of the oilthat the rubber is kept sufiiciently soft and spongy for reworking andrecompounding. It also is important that in the digesting steps of theprocess, the oil should not impart permanently to the rubber suchexcessive tackiness as seriously to interfere with working the stock.

It is the object of our invention so to conduct a reclaiming process onnatural rubber, using. a novel reclaiming oil which we have foundpartlcularly desirable for the purpose; and so to relate the conditionsof the process to the novel oil that the reclaimed stock is in goodcondition for working and works well in the rolls, being neither dry andfriable nor unduly mushy or tacky.

Another object of our invention is to use such oil and so to adjust theconditions of the process to its use, that we obtain as a product areclaimed rubber of improved sort, because of the ability of thereclaiming oil to take up free sulphur for removal from the stock, andbecause of the property of the oil in leaving some softening content ofrelatively high boiling oil in the reclaimed rubber.

Primarily we have discovered that an ideal oil for use in rubberreclaiming may be blended from two unlike oils, one such componentconsisting of the resin-forming unsaturates obtained from coke ovenlight oil in unpolymerized condition, and the other component being oneof the aliphatic hydrocarbon oils derived from the distillation ofpetroleum oil. As derived from petroleum the allphatic oil may consisteither of paraffins or of olefins without substantial resin-formingunsaturation. The resin-forming unsaturates are obtained by distillationof crude light oil which comes over before tar in the by-product cokingof coal, and are contained in the coumarone-indene and xylene out, whichcontains only such proportion of aromatics devoid of resin-formingunsaturation as are normally included in distillation conducted on acommercial scale.

We are aware that aliphatic hydrocarbon oils have been used as acomponent of rubber-reclaiming oils, being associated therein with cutsconsisting chiefly of the aromatics which are devoid of resin-formingproperties and naphthalene, or with the naphthenic oils derived as wasteproducts in the solvent refining of petroleum oils. Also we are awarethat prior rubber-reclaiming oils have incidentally contained some smallproportion of resin-forming unsaturates within their prescribed boilingranges; and that the prior art has utilized the lower polymers ofresin-forming unsaturates in rubber reclaiming to exert a dissolving andsoftening effect on the scrap rubber. We do, however, believe ourselvesto be the first to discover the advantages of the unpolymerizedresin-forming unsaturates of coke oven light oil as a component of arubber-reclaiming oil. Thus we have discovered that the chemicalstructure of the resin-forming unsaturates of coke oven light oil givesthem particularly high surface tension with attendant high penetrativeproperties. In pursuance of that discovery, additionally 'We have foundthat by use of such resin-forming unsaturates as the penetrative andswelling content of a rubber-reclaiming oil we are able to penetrate andenduringly to swell the particles of the rubber stock which are openedup in the digesting treatment. Penetration of the rubber stock by thecomposite oil serves also to admit to the interior of the particles asoftening content of aliphatic hydrocarbon oil to an extent notpreviously attained in the art. The softening effect thus obtainedendures to give a high grade of reclaimed rubber after the working andrecompounding. It is essential in the composition of ourrubber-reclaiming oil .that the resin-forming unsaturates be inunpolymerized condition, because even the lowest polymers of suchunsaturates, although they have fair solvent power, are so lacking inpenetrative properties that they are incapable of performing effectivelythe desired function of entering and swelling the rubber particles, andcan be used only in large quantity to soften the rubber or wholly todissolve it.

In obtaining from coke oven light oil the resinformi-ng unsaturatesforming one component of the rubber-reclaiming oil we take such cut thatit consists more than 50% of one or more of the resin-formingunsaturates styrene, coumarone and indene. Such cut of crude coke ovenlight oil may be either toward the styrene end containing but littlecoumarone and indene, or toward the coumarone and indene end containinglittle or no styrene. Within the limits of the distillation range,however, the cut is composed preponderantly of these resin-formingunsaturates.

Thus we take the cut of coke oven light oil which boils within thapproximate range of 120 C. to 265 C., and which boils over 60% withinthe approximate range of 135 C. to 210 C., or any distillation fractionof that cut. This cut, or any fraction thereof boiling at least 60%below 210 C. consists over 50% of resin-forming unsaturates, eithercoumarone and indene or styrene, or mixtures of those resin-formingunsaturates. It is possible by careful treatment to obtain within thecut a low boiling oil which consists in substantial entirety ofresin-forming unsaturates. In practical effect, and in accordance withcommercial considerations, however, it is generally desirable to acceptsuch cuts coming within the prescribed range as have more than 50% ofthe resin-forming unsaturates without seeking to obtain approximateperfection in their composition.

As the aliphatic content of the blend we use a petroleum naphtha, oranalogous petroleum cut distilling within the approximate range of about200 C. to 280 C. Using this aliphatic oil within our contemplatedproportion range gives a blend having an adequately high flash point forsafe use in the rubber-reclaiming process.

It is to be understood that the aliphatic hydrocarbon oil from thedistillation of petroleum oil distilling within the approximate range of200 C. to 280 C. may contain those cyclo-paraffins known as naphthenes,and may contain olefins as well as paraflins, and by aliphatichydrocarbon oil from the distillation of petroleum we inherently mean anoil obtained from the distillation of petroleum without such treatmentas to produce any substantial content of cyclic compounds. Also by suchterm used in distinction from the resin-forming unsaturates forming onecomponent of our reclaiming oil, we mean an oil which though it may beolefinic rather than paraflinic is not resin-forming by virtue of thediene structure as are the diolefins.

It should be understood that in the composition the content ofresin-forming unsaturates performs the function of penetrating andswelling the rubber. This function the resin-forming unsaturates areparticularly well suited to perform, because their chemical structuregives them high surface tension which causes them to creep over thesurfaces of the individual particles of a mass of reclaiming stock inthe digestor. In the proportioning suited to the rubber stock which isbeing reclaimed and the conditions of the process the aliphatichydrocarbon oil does not detract from that power of penetration. On thecontrary the penetrative ability of the unpolymerized resinformingunsaturates serves suitably to introduce the softening content ofaliphatic oil into the body of the scrap rubber to prepare a reclaimstock in good condition for working. The nonresin-forming content of thelight oil out; that is, the content of mono-nuclear and poly-nuclearbenzene ring compounds which do not possess such conjugate unsaturationas to render them resin-forming, such as benzol, toluol, xylol, cumeneand pseude-cumene, are relatively undesirable as compared with theresin-forming content of the cut. This is for the reason that while suchsubstances have good solvent power, they lack the high surface tensionand penetrative property which goes with the chemical structure of theresin-forming unsaturates of coke oven light oil.

From a different viewpoint, the high penetrative properties of theresin-forming unsaturates permit them to be used in a smaller proportionwith respect to the content of aliphatic oil in the blend than is thecase with the compounds of the coke oven light oil and analogouscompounds, which do not have resin-forming unsaturation. The highproportion of resin-forming unsaturates functions in the process to givea reclaiming oil which desirably softens the rubber for working withoutmaking it persistently tacky. Also with a blend having a satisfactorycontent of resin-forming unsaturates with respect to the aliphatichydrocarbon oil a low total proportion of the reclaiming oil can be usedeffectively. Y

Taking the prescribed cut boiling over 60% within the approximatelyrange of 135 C. to 210 C. having a concentration of more than 50%resin-forming unsaturates, we can blend it with the aliphatichydrocarbon oil in a varied proportion of 50% to of the resin-formingunsaturate cut with 20% to 50% of the aliphatic hydrocarbon oil.

A reclaiming oil consisting about 60% of a cut of crude coke oven lightoil boiling over 60% within the approximate range of C. to 210 C., andwhich has therefore a resin-forming content over 50%, with about 40% ofthe aliphatic hydrocarbon oil boiling within the approximate range of200C. to 280 C., may be considered to be our standard compositionpreferred for the reason that it is best adapted to conform to varyingconditions in rubber reclaiming. If we assume an efiiciently conductedrubber-digestingprocess utilizing a steam pressure of from about lbs. to250 lbs., or more, for reclaiming what may be considered a high grade ofscrap rubber, the reclaiming oil desirably is used in a quantity equalto about 4% to 10% the weight of the rubber for summer temperatures, andabout 6% to 12% the weight of the-rubber for wintertemperatures.

It may be explained, that in modern reclaiming practice there are twogenerally accepted methods of digesting the scrap rubber. In theautoclave,

or wet, process highsteam pressure with the high temperature attendanton it is used, initially to soften and open up the particles of rubbersubjected to digestion. In the pan process of digestion heat is usedinitially to soften the rubber, and the pressure of vapors generatedunder the influence of the heat serves to open up and swell theparticles. In present day practice, the autoclave process is used whenthe scrap rubber may retain some content of fabric after it has beenscreened, and that process is preferred if the rubber is difficult tobring into workable condition and a high grade of reclaimed rubber isrequired. The pan process is used only on scrap rubber which has noretained fiber content. It thus may be used satisfactorily in reclaimingscrap rubber from the inner tubes of vehicle tires which is easilyreclaimable; and scrap rubber from mechanical goods in which thereclaimed product need not be brought to a particularly high order ofsoftness and flexibility.

In practice under both variants of the digestion process, the conditionsvary widely in accordance with the specific properties of the scrapwhich is subjected to digestion. Assuming that all the scrap with whichwe are here concerned consists wholly of natural rubber, there is nonethe less great variation in the severity of the treatment required tobring different grades of rubber such as rubber from the shoes ofvehicle tires, scrap from mechanical goods, and the like into conditionfor reworking. The time of treatment, the steam pressure employed in anautoclave digestion, and the like factors are therefore to be consideredas variables.

Under present day practice the steam pressure employed varies from about160 lbs. to 250 lbs. and the time of treatment from about hours to 40hours. There is, however, a current tendency toward even higher steampressures with a corresponding decrease in the length of time requiredfor digesting the scrap, and the employment of steam pressuressubstantially exceeding 250 lbs. is in immediate contemplation. It isalso the current tendency in the trade to make the pan process moreefficient by increasing the temperature of the treatment, and byincreasing the quantity and effectiveness of the reclaiming oil used init. In accordance with the, best current practice in digesting by thepan process, we use temperatures of from about 300 F. to 500 F. and thetime of treatment is from about 7 hours to hours. It may be notedgenerally that in preparing the scrap rubber for digestion it usually isground to a, size which will pass through screens of 3 to .5 meshes tothe inch. A 3 mesh screen size may be used satisfactorily for digestionin an autoclave, but a 5 mesh screen size is preferable for pandigestion. Also assuming that rubber of the same characteristics istreated alternatively in an autoclave or by pan digestion, about 15% tomore reclaiming oil is used in the pan process than in the autoclave.

It readily will be understood that our novel reclaiming oil, because ofits property of high penetration and its ability readily to complete theswelling of the rubber and enduringly to swell it, is peculiarly welladapted to use in reclaiming practice as that practice develops towardhigher efficiency and decreased time for digestion.

To give a typical exemplification of a reclaiming process in accordancewith our invention, a sub-- stantial weight of vehicle tires was takenas the starting material. These tires were cut into relatively smallpieces, withoutattempting to segregate the different component parts ofthe tires. The stock was then ground fine enough to pass through ascreen of 3 meshes to the inch and was fluffed and air blown, to removemost of its fiber content. It then was passed under magnets, to removenails and other pieces and particles.

The mass of. rubber particles for reclaiming then was mixed mechanicallywith the rubber-reclaiming oil composed of the crude resinbearing cokeoven light oil out and 35% of petroleum naphtha, in a quantity equal to7% the weight of the rubber. The mass, carrying the reclaiming oil wasintroduced into an autoclave, together wtih about 3% its weight of a 20%caustic soda solution, Steam was run in to build up a steam pressure ofabout 200 lbs. per square inch and a corresponding.temperature. About '7hours was spent in heating up the batch, and it then was held at thattemperature for about 12 hours. The batch then was allowed to coast andcool.

After the batch had cooled sufiiciently, the upper valve of theautoclave was released and vapors were blown off. These vapors consistedlargely of the lighter end of the coke oven light oil cut, some of theheavier end of that component and a large proportion of the petroleumnaphtha being retained by the rubber. The bottom valve of the autoclavewas then opened and the moisture and alkali were drained off. It may benoted that in passing off as vapors, the resin-forming unsaturates ofthe reclaiming oil carry with them the content of free sulphur whichthey have absorbed.

At this stage of the complete process tailings were removed andtack-increasing and cornpounding ingredients were added. It is to benoted that some smoothing agent additional to that provided by theretained heavy end of the reclaiming oil may be included in this stage.The stock thenwent to mills, where it was worked and sheeted.

Specifically, the reclaiming oil used in the above procedure had as itspenetrative and swelling component a coke oven light oil out boilingabout below 210 C.

The reclaiming oil described above is of even greater utility inconducting a reclaimin opera tion by the pan process of digestion. Infollowing procedure in accordance with our invention in which highpressure steam was not used, initially the rubber scrap for reclaimingwas cut and ground to pass through a screen of 5 meshes to the inch.This reclaim stock was of selected fabric-free sort, being a scrapnatural rubber from the inner tubes of vehicle tires. The mass of rubberparticles for reclaiming then was mixed mechanically with therubber-reclaiming oil in a, quantity of the oil equal to 10% the weightor" the rubber. Specifically, the oil used was com posed of the cruderesin-bearing coke oven light oil out and 25% of petroleum naphtha. Thecoke oven light oil cut providing the penetrative and swelling componentof the oil was a cut boiling about below 210 C. Thus it will be seenthat for this variant of the reclaiming process the reclaiming oil isused in increased proportions and also is socomposed as to contain ahigher proportion of lighter volatiles.

The ground reclaim stock with its coating of oil then was placedin largepans and the pans were racked in an oven. As is desirable, some waterwas held near the bottom of the oven to prevent scorching. The oven wasclosed to render it substantially. airtight. and heat was applied. Thetemperature of the oven was raised sufliciently,

that is to about 350 to vaporize the more volatile componentsof the'oil,and tobuild'up. a substantial pressure of those vaporsin the. oven. Thetreatment was continued for about 10 hours, at which time the oven wasopened and the vapors permitted to escape.

By using an adequate quantity of! the oil, greater than that required inan autoclave to digest the same scrap there is suflicient pressure ofthe vapors from the oil adequately to penetrate and to carry forward theswelling of the rubber. It has been noted that we prefer, in thedigesting procedure involving the use of pansrather than an autoclave,to use reclaiming oil having a greater proportion of lower boilingcomponents, and to use the oil in a proportion from 30% to 50%v greaterthan when used inautoclave work; That is a quantity equal to from aboutto 18% the weight of the rubber.

After removal from the oven, the further treatment of the reclaim wasidentical with thatdescribed above with respect to stock which hadbeendigested in an autoclave.

The ability of the resin-forming unsaturates to absorb sulphur duringthe digestion of t the rubber is an important property. They have thecapacity to take up sulphur at any conjugated double bond of theirstructure at temperatures no higher than from about 140 C. to 180 0.,which temperatures are exceeded in the best standard processes of rubberreclamation. By

their ability to absorb sulphur they tend to place the reclaim rubber inbetter condition for recompounding, because when pressure. is releasedat the end of the digestion stage of the reclaiming process theresin-forming unsaturatesvaporize 01f carrying with them the sulphurwhich they have absorbed. It may be noted at this point that the higherboiling aliphatic hydrocarbon oil tends to remain in the rubber stock,enduringly tosoften and smooth it. Because the cut boiling below 210 C.has the best odor of any of thecoke oven light oil cuts, and because ofthe aliphatic content. of the reclaiming oil, its use givesthereclaimedrubber a better odor than do most reclaiming oils commonlyin use.

In the digestion process itself the high surface tension possessed bythe resin-forming unsaturates gives them not only high penetratingpower, but also the ability to coat thesurfaces of particles of rubberdiiTering in size. digestion of the stock the higher boiling aliphatic-oil provides in and on the particles of rubber a drying agent which atthe end of the digestion leaves the stock in a condition which is nottoo tacky for working. The drying, softening and smoothing effects ofthe higher boiling aliphatic hydrocarbon oils are of great importance.While those properties of such oils are well known they are renderedavailable in our rubber-reclaiming; oil in an order not previouslyattained. This is for the reason that the high penetrativerproperty ofthe resin-forming unsaturates allows an increasedproportion of thealiphatic oils tobe used with a cut consisting essentially of thoseresin-forming unsaturates, so that full advantage of the desir-- able.properties of the aliphatic hydrocarbon oils may be had while yetobtaining the necessary swelling and initial softening'of the rubberstock for recompounding. It will be understood that the effect of theresin-forming unsaturates themselves on the rubber is an activesoftening. efiect,

and their use without a substantial proportion of aliphatic hydrocarbonoil with its tendency to dry as well as permanently. tosoften thestoclcIn thewould giveasaproduct of digestion azmass of rubher: tooincoherent", pasty and: tacky to be. in a;

condition suitable for working.

We havefound that any wellknown single substance selected ascombiningthe penetrative and swelling action. of the resin-forming unsaturatesofthe. crude (unpolymerized) cutand. the drying and permanent softeningefiect of the; aliphatic hydrocarbon oil' is unsatisfactory in practice.Thusoils composed of the dimers of coumarone and indene or styrene inthe lowest stageof polymerizationof those substances, while havinggoodsolvent power, donot have good ability to penetrate-and swellv therubber. Their effect in the digestion process is, therefore, to give astock for recompounding in which the particleseither remain unsoftenedinteriorly, or in. which. the digestor batch as a whole is reduced to'anunworkable mushy or tacky condition. The same is true of various otherrelatively highboiling oils, such as pine oil, tar oil, naphthenicciland the dimers of the. resin-forming unsaturates of' turpentineand-petroleum.

We claim as our invention:

1. The method of digesting scrap rubber for reclaiming by subjecting thescrap rubber in finely divided condition to heat and; the pressure ofvapors in a closed vessel at a temperature from about 300 F; to 500 1for from about? to 40 hours in contact with about 4% to 18% its weightof an oil composed about 50% to of a cut ofcrude coke oven light oilboiling more than. 60 within the approximaterange of C. to 210 C. andcontaining over 50% of unpolymerized resin-forming unsaturates and about20 to 80% of a: non-resin-formingaliphatic hydrocarbonoil from thedistillation of petroleum oil boilingwithin the approximate range-of 200C. to-280 C'.

2. The method of digesting scrap rubber for reclaiming by subjecting thesaid scrap rubber in finely. divided condition wheat and the pressure ofvapors ina closed vessel at atemperature from about 300 F. to 500 F. forfrom about 7 to 40 hoursincontact with-about 4% to 18% its weight of anoil composed about 60% of a cut of crude coke oven light-oil boilingmore than 60% within the approximate range'of'135'C. to'210 C. andcontaining over- 50 of unpolymerized resinforming unsaturatesand about40% of a nonresin-forming aliphatic hydrocarbon oil from thedistillation of petroleum oil boiling within the approximate range of200 C. to 280 C.

3. A rubber-reclaiming oil'consistingin substantialentiretyof ablendcomposedabout 50% to 80% of a cut of. coke oven light oil boilingmore than 60% within'the approximate range of 135 C. to 210 C.andconsisting over 50% of unpolymerized resin-forming. unsaturates, andabout 20%v to 50% of anoneresin-f'ormingaliphatichydrocarbon oilfromthedistillation ofrpetroleum oilboiling'within the approximate rangeof 200 C. to 280 C.

4. A rubber-reclaiming oil consisting in substantial entirety of ablendcomposed about 60 %.of

- a cut of coke oven light oil boilingimore than 60% within theapproximate range of 135 C. to 210 C. and consisting over 50% ofunpolymerized resinforming unsaturates, and about 40% of anonresin-forming aliphatichydrocarbon oil from the distillation ofpetroleum oil boiling v within. the approximate range of 200 C. to. 280C- CHARLES. H." CAMPBELL. ROBERT W. OSTERMAYER.

(References on following page) Number Name Date REFERENCES CITED2,069,929 Swanberg Feb, 9, 1937 The following references are of recordin the 2,081,448 Carmody May 25, 1937 fi of this t t: 2,145,341 CampbellJan, 1, 19 1 TE PATENTS 5 ,57 CaImOdY Mar. '7, 1939 UN TED STA S2,244,654 Rostler et a1 June 3, 1941 32 0 m ky J 3 2,381,506 Loane Aug.7, 1945 s roxms ens an. 1,793,161 Cowdery Feb. 17, 1931 OTHER REFERENCES2,021,046 Campbell 1935 10 Whitehead, Benzol (1920), pages 165 and2,069,927 Rhodes et a1 Feb. 9, 1937 195.

